1. Field of the Invention
The present invention relates to the field of semiconductor processing, wherein integrated circuits and other devices are formed on a substrate. More particularly, the present invention relates to processing chambers useful for forming microelectronic devices on semiconductor wafers and other substrates.
2. Background of the Art
Semiconductor processing chambers are used to provide process environments for the fabrication of integrated circuits and other semiconductor devices on wafers. To form the integrated circuits on the wafers, they may be sequentially processed, first in a deposition chamber in which a film layer of a metal, dielectric or insulator material is deposited on the wafer, then in a lithographic process chamber wherein a mask is formed on the deposited film layer, and then in an etch chamber where selected portions of the previously deposited film layer are etched. One or more ion implant and passivation steps may also be used to process the wafer. By repetitively depositing a film layer on the wafer, forming a mask over the film layer, and then selectively etching areas of the film layer exposed by the mask, an integrated circuit device may be fabricated on the wafer.
Most prior art semiconductor etch and deposition chambers have several common features. For example, most such chambers are built around a vacuum enclosure in which the wafer is received for processing. A gas inlet having a mass flow controller, and a throttled exhaust coupled to a vacuum pump through a gate valve, communicate with the chamber enclosure to provide the process gas flow and the vacuum conditions necessary for wafer processing. A wafer support member is located within the enclosure to provide a secure resting place for the wafer in the enclosure during the deposition or etch process. A slit valve extends through the enclosure wall to allow a robot blade to place the wafer on, and remove the wafer from, the support member.
To perform the etch or deposition process step in the chamber, a process gas is flowed through the vacuum enclosure. The gas may, as with chemical vapor deposition, deposit a film on the wafer, or the gas may provide disassociated gas atoms which, when exposed to an electric field in the enclosure, are excited into a plasma. The plasma may form an etch plasma to selectively etch a film layer already deposited on the wafer, or the plasma may be used to sputter a target, as with physical vapor deposition, to provide material to form a deposition film layer on the wafer. After the film layer is deposited on the wafer, or after the deposition layer previously formed on the wafer is etched, the process gas is evacuated from the enclosure and the wafer is removed from the enclosure through the slit valve.
During each of the aforementioned processes, a film layer is also formed on the exposed surfaces of the enclosure, including the surfaces of the enclosure walls, the support member, the slit valve, the enclosure inlet, and even within chamber support equipment including the enclosure exhaust, and the pump. The film layer formed on the chamber surfaces may, as with deposition processes, be primarily comprised of the deposition layer material, or, as with etch processes, may be primarily comprised of by-products of etching. This film layer is friable and, if left in place, could form contaminant particles in the enclosure which could deposit on the wafer. Where a contaminant particle of sufficient size deposits on a wafer, one or more semiconductor devices being formed on the wafer will be defective. Therefore, the enclosure must be periodically cleaned to remove these contaminants.
To clean the interior surfaces of the chamber, the cover, or another access panel, of the vacuum enclosure is removed to expose the interior surfaces of the enclosure. The film layer formed on the interior walls and other surfaces of the enclosure is then cleaned with water and/or other materials. Additionally, the other chamber components that may be exposed to the process environment, such as the vacuum pump and the throttle valve, are also removed from the chamber so that the interior pump and valve surfaces may be cleaned. After cleaning, the pump, valves and cover are replaced, and the enclosure is again pumped down to the operating pressure. Because water is used to clean the enclosure surfaces, and water is adsorbed on the metallic enclosure surfaces during the cleaning process, the water must be removed from the enclosure before a satisfactory, stable, vacuum pressure can be maintained in the chamber. Therefore, the chamber is "baked out", at an elevated temperature, to help drive the water from the enclosure surfaces and thus provide a "dry" enclosure environment in which a stable vacuum may be maintained. This bake out period typically lasts at least 8 hours.
The time required to clean and bake out the process chamber is "down time" for the user of the process chamber, because no wafer processing can occur in the chamber during these periods. The amount of chamber down time is further compounded when the process chamber is coupled to multiple other process chambers through a transfer chamber, and the process chamber slit valve must be cleaned. The slit valve must be open during at least a period of the time it is being cleaned. Because the process chamber cover is removed to provide access to the slit valve, the open slit valve communicates ambient conditions to the transfer chamber when it is cleaned. Additionally, water or other materials may contact the transfer chamber surfaces when the slit valve is open during cleaning of the slit valve or chamber, thereby necessitating bake out of the transfer chamber to achieve a stable vacuum after the process chamber is cleaned and resealed. During the period of time that the slit valve is open to the transfer chamber, communication between the transfer chamber and all of the other process chambers must be interrupted to ensure that the cleaning of the one process chamber does not contaminate any of the other process chambers linked to the transfer chamber. Therefore, each of the other process chambers linked to the transfer chambers cannot be used while the process chamber slit valve is being cleaned, or, only those wafers already placed in the other process chambers at the time the slit valve is opened can be processed, and those wafers cannot be removed from the other process chambers until the slit valve is closed to isolate the transfer chamber and the transfer chamber is pumped down and, if necessary, baked out.
In addition to the down time attributable to the cleaning and baking out of the process chamber, many chamber maintenance procedures contribute to chamber down time. For example, servicing of the pump and the pump throttle valve often contributes to down time. In the typical prior art process chamber, the throttle valve is located intermediate of the chamber enclosure and the pump. If the throttle valve must be serviced, or must be cleaned without the need to clean the pump, the pump must still be removed to provide access to the throttle valve. The time needed to remove the pump and the throttle valve is substantially greater than would be necessary to remove the throttle valve alone, and this time difference contributes to chamber downtime. Additionally, once the pump is removed from the chamber, and the interior surfaces thereof are exposed to the atmosphere, the pump itself must be baked out or otherwise stabilized before the pump can maintain a stable vacuum pressure.
The existence of moving parts within the chamber enclosure, such as the intermediate wafer support used to transfer the wafer from a robot blade to the support member, are also a source of chamber down time. The moveable parts within the chamber enclosure receive a deposition or contaminant layer during the use of the chamber because they are exposed to the process environment within the chamber. This contaminant layer is a primary source of particle contaminants on the wafer because the movement of these parts tends to free portions of the contaminant layer deposited thereon during processing. Therefore, these surfaces must be periodically cleaned which increases the time needed to clean the chamber.
One prior art device known to applicants maintained a process environment in a separate compartment from the substrate loading environment, and thus at least partially isolated the process environment from the substrate loading equipment used to position the substrates on a support member. This multi-station device, known as an Eclipse sputter tool which has been available from MRC, included a large main chamber connected, through a fire wall, to a plurality of separate processing stations. Each processing station was located on the exterior of the firewall over a chamber aperture. A plurality of substrate heaters were located within the main chamber, and each heater was dedicated to a particular processing station. A large rotatable transfer plate, having a plurality of apertures therein, was located substantially parallel to the firewall. A substrate could be supported within each of the apertures in the rotating plate, so that each substrate could be moved within the main chamber to be positioned in alignment with each of the firewall apertures, and thus in alignment with each of the processing stations.
The MRC multi-station tool was used to sequentially process substrates through one or more of the processing stations, wherein a sputter environment is maintained in each of the processing stations. In operation, the substrates were loaded into the apertures in the rotating plate at a load position, and rotated through the entire multi-station tool for processing. To perform the processing steps on the substrates, the substrates are first aligned over the individual processing stations, and the substrate heaters were moved from a retracted position within the main chamber to an extended position. The heaters included a plate portion, which engaged the backside of the substrates within the rotating wall apertures to heat the substrates, and an extending annular wall, which engaged against the rotating plate and pressed the rotating plate against the firewall. Seals were provided at the interface of the annular wall against the rotating plate, and between the rotating plate and the firewall, to create a sealed station for the sputter process. Once all of the heaters were moved into their extended positions, a sputter deposition environment would be created in each of the process stations. After the process was completed in the process stations, each of the heaters were retracted from their respective process chambers and the rotating plate was rotated to position the substrates at the next processing station.
The configuration of the MRC multi-station tool has several inherent limitations. In particular, the tool is inherently prone to cross-contamination between the stations, because a portion of the rotating plate is exposed to each process environment as the substrates are rotated for processing in each of the processing stations. Thus, where different materials are deposited on the substrates in different processing stations, impurities, consisting of materials other than those present in the specific processing stations, can enter the main chamber when released from the rotating plate. Additionally, trace amounts of the process environment maintained in each of the processing stations would be discharged into the main chamber when the heaters are retracted from the individual processing stations. These trace amounts of contaminants commingle and build up in the main chamber and in the process stations, to the point where the entire multi-station tool, including the large main chamber, must be cleaned to prevent contamination of the process environments maintained in the individual processing stations. Finally, the tool is slow in operation, because throughput is limited by the slowest process being performed in the tool.
There exists a need in the art for a processing chamber in which the turnaround time for chamber cleaning is reduced, and an arrangement wherein multiple chambers may be connected to a transfer chamber yet the cleaning of a given chamber does not require other chambers connected to the transfer chamber to be shut down for the cleaning of the process chamber.